Our studies during the past several years have indicated that there is intact absorption of dipeptides, such as glycylglycine and glycylleucine, and a tripeptide, such as triglycine, in human intestine. The absorption of these oligopeptides appears to be mediated by a common carrier system separate from those for free amino acids. A wide range of experiments using in situ perfusion techniques in human intestine have been proposed. These studies have been designed to include the investigation of the following: (1) the extent of intraluminal and surface hydrolysis of oligopeptides as a mechanism for peptide disappearance; (2) the importance of intact absorption for a wide range of oligopeptides with different amino acid residues containing basic, acidic, and neutral amino acids; (3) the heterogeneity of carrier systems for oligopeptide transport; (4) the size of peptide molecules that restrict penetration by mucosal cells; (5) the effect of altered nutrition on the transport and hydrolysis of oligopeptides in vivo; and (6) the effect of the bypass operation on the intestinal transport of free amino acids and oligopeptides in man. Preliminary investigations in our laboratory have shown that there is efficient utilization of dipeptides such as glycylglycine or glycylleucine when administered intravenously in rats. In vitro and in vivo experiments have been proposed to study the metabolism of a wide range of oligopeptides differing in amino acid constituents and molecular sizes when administered intravenously in rats. Biochemical and physiological processes concerned with the hydrolysis and transport of these oligopeptides by the liver and the skeletal muscle will be explored. The results of these studies will be ultimately used to design new, more effective, and practical methods to provide amino acids orally and parenterally to patients in need of maintenance or improvement of their protein nutrition.